JP2005136620A - Signal demodulator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a signal demodulator which can demodulate an amplitude modulation signal and a phase modulation signal by using a common circuit of a simple structure. <P>SOLUTION: An orthogonal detection circuit 3 used for demodulating a phase modulation signal is used. Each multiplier 31 and 32 multiplies a received amplitude modulation signal by the cosine component and the sine component of a non-modulation signal whose frequency is the same as a carrier generated by an oscillator 33. High-frequency filters 41 and 42 remove high-frequency components of the output, and a vector operation circuit 5 takes a mean square so as to acquire amplitude information. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a signal demodulator, and relates to, for example, an amplitude modulation signal such as an ASK (Amplitude Shift Keying) modulation method signal and a QPSK (Quadrature Phase Shift Keying) modulation used in a DSRC (Dedicated Short Range Communication) system. The present invention relates to a signal demodulator capable of modulating both phase modulation signals such as one-way signals.

  In a DSRC system used for road-to-vehicle communication such as an ETC or a commercial vehicle management system, two modulation methods of an ASK modulation method and a QPSK modulation method are mainly used in a mixed manner. Therefore, it is necessary to provide a communication apparatus on the vehicle-mounted side with a system that demodulates two types of signals having different modulation methods. Conventionally, a demodulation unit for an ASK modulation signal and a demodulation unit for a QPSK modulation signal are provided independently, and switching is performed according to the signal to be demodulated. However, if an independent demodulation circuit is provided for each modulation method, the circuit configuration becomes complicated and the cost increases. In view of this, development of a technique for sharing a demodulation circuit of a different modulation method is being promoted (see, for example, Patent Documents 1 and 2).

Japanese Patent Application Laid-Open No. 2004-228867 makes it possible to demodulate various modulation signals by switching programs by digitizing a received signal and performing demodulation by digital calculation. Patent Document 2 relates to sharing of demodulation circuits of MSK (Minimum Shift Keying) modulation method and QPSK modulation method.
JP 2003-78577 A JP 2000-134271 A

  However, since both MSK modulation and QPSK modulation are frequency modulation schemes in common, it is easy to realize circuit sharing as in the technique described in Patent Document 2, but ASK modulation is It differs in that it is amplitude modulation, and the demodulation method is fundamentally different. Further, according to the technique of Patent Document 1, since decoding of various modulation methods is performed by software, it is possible to decode amplitude modulation and frequency modulation by a common device. However, in the DSRC system, there are areas for communication. Since it is necessary to process a relatively large amount of data in a short time and in real time, a processor and a memory that perform processing at a high speed are required, which complicates the apparatus configuration and increases the cost.

  Accordingly, an object of the present invention is to provide a signal demodulating device capable of demodulating both an amplitude modulation signal and a phase modulation signal by a common circuit having a simple configuration.

  In order to solve the above problems, a signal demodulating device according to the present invention is a signal demodulating device having a quadrature detection circuit and a signal processing circuit, wherein a high frequency component is obtained from each of an in-phase component and a quadrature component output from the quadrature detection circuit. The signal processing circuit has a high frequency filter to be removed, and when the amplitude modulation signal is input, the signal processing circuit acquires the amplitude component of the amplitude modulation signal based on the in-phase component output after passing through the high frequency filter.

  Alternatively, the signal processing circuit preferably acquires the amplitude component of the amplitude modulation signal based on the mean square of the in-phase component and the quadrature component after passing through the high-frequency filter when the amplitude modulation signal is input.

  In the quadrature detection circuit, the input signal is branched into two, and one is multiplied by the COS component of the unmodulated signal having the same frequency as the carrier wave, and the other is multiplied by the SIN component of the unmodulated signal having the same frequency as the carrier wave. Among the multiplication results, the former is called an in-phase component, and the latter is called a quadrature component. When the input signal is phase modulated like a QPSK modulated signal, the phase of the signal is detected from the in-phase component and the quadrature component. On the other hand, when the input signal is an amplitude modulation signal, for example, an ASK modulation signal (A × cos (2πft + θ)), the former is A × cos (2πft + θ) × cos (2πft) = A / 2 × {cos (4πft + θ) + cosθ} In the latter case, A × cos (2πft + θ) × sin (2πft) = A / 2 × {sin (4πft + θ) + sinθ}. When cos (4πft + θ) and sin (4πft + θ), which are high-frequency components, are removed by a high-frequency filter, they pass through. The latter output is A / 2 × cos θ for the former and A / 2 × sin θ for the latter. In general, θ≈0 and cos θ≈1, so the former is approximately equal to A / 2.

When θ ≠ 0 due to frequency deviation, the root mean square of the former and the latter is taken. The root mean square is {square root} {(A / 2 × cos θ) ² + (A / 2 × sin θ) ² }, which is the absolute value of A / 2.

  Furthermore, it is preferable to provide an amplifier that amplifies the received amplitude modulation signal in accordance with the obtained amplitude. That is, the amplification gain is controlled according to the amplitude.

  By guiding the output of the quadrature detection circuit to a high-frequency filter and passing it through to remove the high-frequency component, amplitude information of the amplitude-modulated signal can be extracted by a quadrature detection circuit used for demodulation of a phase-modulated signal such as a QPSK modulation method. . For this reason, there is no need to provide a dedicated circuit (envelope detection circuit) for demodulation of the amplitude modulation signal, and the demodulation circuit can be shared, so that the configuration is simplified and the cost can be reduced.

  In particular, when the mean square is used, it is possible to perform demodulation with low noise without being affected by the frequency deviation.

  By using the root mean square for gain adjustment when receiving an amplitude modulation signal, gain adjustment based on amplitude information is possible, and gain adjustment that is not affected by a carrier wave is possible.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings. In order to facilitate the understanding of the description, the same reference numerals are given to the same components in the drawings as much as possible, and duplicate descriptions are omitted.

  FIG. 1 is a block diagram showing a main configuration of a receiving unit of an in-vehicle communication device provided with a signal demodulator according to the present invention, and FIG. 2 is an image diagram of a DSRC system in which the in-vehicle communication device is used.

  The receiving unit of this communication apparatus includes a signal demodulating apparatus 100 according to the present invention, and includes an antenna 1, an amplifier 2, a quadrature detection circuit 3, high frequency filters 41 and 42, a vector calculation circuit 5, and an AGC. (Auto Gain Control) circuit 6 is formed.

  The antenna 1 and the amplifier 2 are connected, and the output of the amplifier 2 is branched into two and led to the quadrature detection circuit 3. The quadrature detection circuit 3 includes two multipliers 31 and 32 and an oscillator 33, and one input terminal and output terminal of each of the multipliers 31 and 32 are input and output terminals of the quadrature detection circuit 3. Become. The other input terminal of each of the multipliers 31 and 32 is connected to the oscillator 33, and the cos component and sin component of an unmodulated signal having a predetermined frequency are input.

  High frequency filters 41 and 42 are connected to the two output terminals of the quadrature detection circuit 3, respectively, and the output terminals of the high frequency filters 41 and 42 and the input terminal of the vector arithmetic circuit 5 are connected. The output terminal of the vector arithmetic circuit 5 is connected to the input terminal of the AGC circuit 6 and to a signal processing circuit (not shown). The output terminal of the AGC circuit 6 is connected to another input terminal of the amplifier 2 that is also a multiplier.

  As shown in FIG. 2, the DSRC system transmits radio waves 8 from a transceiver 7 installed on the road, and is a communication device installed in a vehicle 9 passing through the transmission / reception area (reception according to the present invention). Communication). For example, a 5.8 MHz band is used as a radio frequency of the DSRC system, and an ASK modulation method and a QPSK modulation method are used in combination as modulation methods.

  Before explaining the operation of the present embodiment, a digital modulation wave used for communication in this receiver will be briefly explained.

  FIG. 3 is a diagram showing modulated waves of ASK modulation, PSK modulation, and FSK modulation together with the original digital signal. As shown in FIG. 3A, the baseband waveform of the original digital signal is a simple binary waveform. In ASK modulation, the amplitude of the modulated wave is varied according to the baseband waveform. For example, as shown in FIG. 3B, there are a region with an amplitude of 0 (base signal is 0) and a region with a constant amplitude (= A) (base signal is 1). On the other hand, in the case of PSK modulation, the amplitude of the modulated wave is always constant as shown in FIG. 3C because only the phase of the modulated wave is switched when the baseband waveform is switched. Also in the case of FSK modulation, the frequency of the modulated wave is switched according to the baseband waveform, so that the amplitude is always constant as shown in FIG.

  FIG. 4 is a diagram showing a modulated wave in the case of QPSK modulation together with a baseband waveform. QPSK modulation is an extension of the PSK modulation shown in FIG. 3 (c), in which two baseband bits are combined and the phase of the modulated wave is varied by π / 4 according to the combined bit value. Thus, this is a transmission method in which four values can be transmitted at a time and the frequency utilization efficiency is improved.

  The quadrature detection circuit 3 in this embodiment is widely used for demodulation of the QPSK modulation method. A specific operation will be described below. First, the demodulation of the QPSK modulation method will be described. The multipliers 31 and 32 multiply the cos component and sin component of the unmodulated signal having the same frequency as the carrier wave of the input signal and pass through the high frequency filters 41 and 42, whereby the in-phase component I and the quadrature component Q can be acquired. FIG. 5 shows the relationship between the in-phase component I and the quadrature component in the QPSK modulation method. Here, a case where 0 is treated as 1 and 1 is treated as 1 in the original digital data is shown. By using the quadrature detection circuit 3, the in-phase component I and the quadrature component Q can be grasped independently.

  When an ASK modulation signal is input, the ASK modulation signal can be expressed by A × cos (2πft + θ) (where A is a value of 0 or 1 depending on the original digital data).

  The output signal processed by the multiplier 31 is A × cos (2πft + θ) × cos (2πft) = A / 2 × {cos (4πft + θ) + cosθ}, and the output signal processed by the multiplier 32 is A × cos. (2πft + θ) × sin (2πft) = A / 2 × {sin (4πft + θ) + sinθ}. By removing (4πft + θ) by the high frequency filters 41 and 42, A / 2 × cos θ and A / 2 × sin θ are obtained as outputs, respectively.

The vector calculation circuit 5 obtains the amplitude A from this output by vector calculation. Specifically, the root mean square of both {{(A / 2 × cos θ) ² + (A / 2 × sin θ) ² }} is taken. Since the root mean square value is | A / 2 |, the amplitude of the ASK modulation signal is obtained, whereby the original data can be demodulated.

  Here, when θ is close to 0, the above outputs are approximately equal to A / 2 and 0, respectively. Therefore, the amplitude of the ASK modulation signal can be obtained without using the vector calculation circuit 5, and the original data can be demodulated. Is possible. However, when there is a frequency deviation and θ is deviated from 0, A / 2 × cos θ, which is an in-phase component output, becomes small, and there is a possibility that correct modulation cannot be performed. In such a case, the frequency deviation component is removed by calculating the mean square value in the vector calculation circuit 5, so that the amplitude can be correctly grasped and demodulated with high accuracy.

  The AGC circuit 6 controls the amplification factor by the amplifier 2 according to the obtained amplitude value A / 2 (see FIG. 6). In the conventional AGC, control is performed according to the signal input to the demodulator, but this is easily affected by fluctuations in cos (2πft + θ) that is a carrier wave. On the other hand, according to the present invention, amplification according to the amplitude value to be obtained is possible, so that gain control efficiency is good and measurement with high accuracy is possible.

  Whether the input modulation signal is an ASK modulation signal or a QPSK modulation signal is determined as follows. In the case of θ≈0, in the case of an ASK modulation signal, the determination can be made because the orthogonal component output is substantially 0 and constant. In addition, even when θ ≠ 0, it is possible to determine the modulation method based on the variation of the mean square value.

  In the above description, the sharing of the QPSK modulation and the ASK modulation has been described. However, the present invention can also be suitably used for the sharing of other phase modulation and amplitude modulation demodulation circuits, and can be applied to in-vehicle communication apparatuses and DSRC systems. The present invention is not limited to this and can be applied to other communication systems.

It is a block block diagram which shows the main structures of the receiving part of the vehicle-mounted communication apparatus provided with the signal demodulation apparatus which concerns on this invention. It is an image figure of the DSRC system in which the vehicle-mounted communication apparatus of FIG. 1 is used. It is a figure which shows both the waveform of the to-be-modulated wave by ASK modulation, FSK modulation, and PSK modulation, and an input wave. It is a figure which shows both the waveform of the modulated wave by an input wave and QPSK modulation. It is a figure which shows the relationship between the in-phase component and quadrature component in a QPSK modulation system. It is a graph explaining the setting of the amplification factor in an AGC circuit.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Antenna, 2 ... Amplifier, 3 ... Quadrature detection circuit, 5 ... Vector arithmetic circuit, 6 ... AGC circuit, 7 ... Transceiver, 8 ... Radio wave, 9 ... Vehicle, 31 ... Multiplier, 32 ... Multiplier, 33 ... Oscillator, 41... High frequency filter, 100.

Claims (3)

A signal demodulator having a quadrature detection circuit and a signal processing circuit,
A high-frequency filter that removes high-frequency components from each of the in-phase and quadrature components output from the quadrature detection circuit;
The signal processing device is characterized in that when the amplitude modulation signal is input, the signal processing circuit acquires the amplitude component of the amplitude modulation signal based on the in-phase component output after passing through the high frequency filter. A signal demodulator having a quadrature detection circuit and a signal processing circuit,
A high-frequency filter that removes a high-frequency component from each of the in-phase component and the quadrature component output from the quadrature detection circuit;
2. The signal demodulator according to claim 1, wherein the signal processing circuit acquires the amplitude component of the amplitude modulation signal from the mean square of the in-phase component and the quadrature component after passing through the high-frequency filter when the amplitude modulation signal is input.   3. The signal demodulator according to claim 1, further comprising an amplifier that amplifies the received amplitude modulation signal in accordance with the obtained amplitude.

Images